Detector for variable pressure areas and an electron microscope comprising a corresponding detector

ABSTRACT

A detector for scanning electron microscopes, which can be used under different pressure conditions in the specimen chamber of the electron microscope, designed for the detection of both electrons and light. For this purpose, the detector has a photodetector and a scintillator of a material transmissive for visible light connected before the photodetector. The scintillator can be provided with a coating transparent to visible light. By the application of different potentials, the detector is suitable for the detection of electrons in high vacuum and for the detection of light with high pressures in the specimen chamber.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a Continuation application of PCT/EP01/07431 claiming priorityof German Patent Applications 100 32 599.8 filed Jul. 7, 2000 and 101 26698.7 filed May 31, 2001.

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The invention relates to a detector for the interaction products,particularly backscattered electrons and secondary electrons, producedin a particle beam device by interaction of a primary beam with a sampleto be investigated.

Usually used for the detection of secondary electrons or backscatteredelectrons in scanning electron microscopes are so-calledEverard-Thornley detectors (ETD), in which the secondary electrons orbackscattered electrons released at the sample interface are attractedaway from the sample to the detector by an extraction grid and thenaccelerated to a scintillator having a high voltage of about 10 kV. Whenthe highly kinetic electrons strike the scintillator, photons areproduced which can be fed to a photodetector, for example aphotomultiplier, by means of a transparent light guide.

Such Everard-Thornley detectors cannot be used with varying gaspressures in the region of the detector, particularly when the ambientpressure of the detector is above 10⁻³ hPa, since the increasedconductivity of the residual gas leads to overstrikes at the highvoltage applied to the scintillator.

At pressures above 10⁻³ hPa in the sample chamber, for indirectdetection of the secondary electrons released by the primary beam, anextraction potential of up to 400 V is applied to an electrode in orderto accelerate the released secondary electrons away from the sample. Agas cascade thereby results from collisions of the secondary electrons.Further, tertiary electrons arise in this gas cascade, and also photonsfrom scintillation effects. Signal detection then takes place either bythe measurement of the electron current or by the detection of thephotons. Corresponding detection principles are described, for example,in U.S. Pat. No. 4,785,182 and WO 98/22971.

Devices which are designed for operation at varying pressure conditionsin the sample chamber, and in which the electron microscopicinvestigation of samples can thus take place both under ultra-highvacuum conditions and also under so-called ambient conditions, in whichthe pressure in the sample chamber is above 10⁻³ hPa, have to havedifferent detectors for the different modes of operation.

From Japanese Patent Document P 11-096956 A, a detector for scanningelectron microscopes is known in which the same photodetector is usedboth for detection of cathode luminescence and also for the detection ofbackscattered electrons. For this purpose, the detector has ascintillator attached to a light guide and having a convex,mirror-coated end. The backscattered electrons penetrate into the mirrorlayer and produce light flashes in the scintillator which are detectedby the photodetector; cathode luminescence, on the other hand, isfocused by the reflecting surface of the scintillator onto another lightinlet surface of the light guide.

In this detector it is however disadvantageous that the scintillator hasto be arranged between the sample and the objective lens of the scanningelectron microscope, so that a correspondingly greater working distanceis necessary between the objective lens and the sample; because of theresulting scattering of the electrons by gas molecules, this detector isunsuitable for uses with high pressures in the sample chamber. Moreover,the scintillator is disturbed by a tilting of the sample.

An Everard-Thornley detector is described in German Patent Document DE40 09 692 A1, its surface being provided with a metal grid. The metalgrid acts, among other things, to prevent the presence of surfacecharges on the non-conducting scintillator. A use of the detector atdifferent pressures in the sample chamber is not mentioned there.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a detectorthat can be used both under high vacuum conditions and also at highpressures in the sample chamber of an electron microscope.

This object is attained by a detector for varying pressure ranges in aspecimen chamber of a particle beam device, wherein the detector isarranged and adapted for detection of electrons and light. Advantageousembodiments of the invention will become apparent from the features ofthe dependent claims.

A detector according to the invention is designed both for the detectionof electrons and for the detection of light. The detection of electronstakes place indirectly here by means of photons produced in ascintillator and subsequently detected in a photodetector.

In an advantageous embodiment example, the scintillator can be placed ata high voltage potential, and is made transmissive for light in aspectral region, preferably in the visible spectral region. For placingthe scintillator at a high voltage potential, the scintillator can beprovided with an electrically conductive coating in grid or strip form.Alternatively, an electrically conductive coating which is transmissivefor visible light can be provided.

The detector is furthermore to have a collector grid which is arrangedon the side of the scintillator remote from the photodetector andlikewise can be placed at a potential. The scintillator and thecollector grid are to capable of being placed at controllable voltagesindependently of each other.

The mode of operation of a corresponding detector under high voltageconditions is analogous to the mode of operation of an Everard-Thornleydetector. For this, the scintillator is acted on with a potential ofabout 10 kV (between 5 kV and 15 kV) under high vacuum conditions, sothat the high-energy electrons striking the scintillator produce photonswhich are then detected by the photodetector. At pressures in the samplechamber above 10⁻³ hPa, either the collector grid or the scintillator,or both, is/are placed at a low potential between 50 V and 1,000 V,preferably between 100 and 500 V, so that the secondary electrons orbackscattered electrons released from the sample by the primaryelectrons produce a gas cascade with scintillation effects on the pathfrom the sample to the scintillator or collector grid. The photonsproduced in the gas cascade are then detected by the photodetector bymeans of the transparent scintillator coating. The value of the voltageapplied to the scintillator or to the collector grid is dependent on thechosen pressure in the sample chamber, and on geometrical factors.

By varying the voltage on the collector grid, it is additionallypossible to differentiate between secondary electrons and electronsbackscattered at the sample. If both the collector grid and thescintillator are at the same potential as the sample, no gas cascadearises and the light signal detected by the photodetector through thetransparent scintillator is a signal that depends exclusively on theelectrons backscattered at the sample.

In a further advantageous embodiment, the detector has a light guide.The light guide can itself consist of scintillator material. Such alight guide serves to efficiently conduct photons produced in thescintillator to the photodetector.

In a further advantageous embodiment, the collector electrode is formedas a needle electrode or as a thin wire. Moreover, further electrodescan be provided, which surround the scintillator and the collectorelectrode in pot form and thereby form in their interior a detectionchamber which communicates with the sample chamber through a smallaperture.

At high pressures in the environment of the detector, in addition to thelight signal, the electron current on the extraction grid and/or on theelectrically conductive coated scintillator can be detected.

BRIEF DESCRIPTION OF THE DRAWINGS

Details of the invention are explained in detail hereinafter using theembodiments shown in the accompanying drawings.

FIG. 1 shows, in section, a sketch of principle of a detector accordingto the invention, in operation in high vacuum;

FIG. 2 shows the detector of FIG. 1 in operation in a pressure rangeabove 10⁻³ hPa;

FIG. 3 shows a further embodiment of the detector according to theinvention in operation in a pressure range above 10⁻³ hPa, and

FIG. 4 shows a third embodiment example of a detector according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The detector in FIG. 1 contains a photodetector (1), for example in theform of a photomultiplier or an avalanche photodiode, and a light guide(2) connected before the photodetector (1), and a scintillator (3)connected to the end face of the light guide (2) remote from thephotodetector (1).

It should be mentioned here that the light guide (2) is not absolutelynecessary, but the scintillator can instead be installed directly beforethe photodetector (1). In this case the photodetector (1) of course hasto be arranged within the specimen chamber of the electron microscope,while with the light guide (2), the photodetector can be arrangedoutside the specimen chamber, since light produced within the specimenchamber is guided by the light guide (2) to the photodetector (1).

Furthermore, it should be mentioned here that the light guide (2) itselfcan also be constructed as a scintillator, so that a separatescintillator layer (3) can be dispensed with.

The scintillator (3) consists of a material transparent to visiblelight, for example, a conventional plastic scintillator. Thescintillator (3) is provided on the side remote from the photodetector(1) with a coating (4) which is electrically conductive and istransmissive for visible light. The electrically conductive coating (4)can be formed for this as a conventional metal layer, which is appliedto the end face of the light guide (2) in grid or strip form or as athin metal film, for example of titanium or gold, having a thicknessbetween 5 nm and 30 nm, preferably a thickness between 3 and 30 nm.Alternatively a transmissive coating with an electrically conductivematerial that is transmissive for light, for example ITO [indium tinoxide], is concerned.

The unit of light guide (2), scintillator (3), and transparent,electrically conductive coating (4) is surrounded by a collector grid(5) at a spacing.

A pressure sensor (12) is arranged in the sample chamber, measures thepressure in the sample chamber, and controls the application ofpotential to the scintillator (3) and/or to the collector grid (5) independence on the chamber pressure, by means of a control (13).

Under high vacuum conditions, i.e. at pressures in the specimen chamberbelow a changeover pressure which is between 10⁻³ hPa and 10⁻² hPa, apotential of 5 kV-15 kV is applied to the scintillator (3) or to theelectrically conductive, transparent coating (4) of the scintillator(3). The collector grid (5), according to whether backscatteredelectrons (BSE) produced at the sample (6) or secondary electrons (SE)produced at the sample (6) are to be detected, has a potential appliedto it of about 400 kV and of reversible polarity. If the detection ofbackscattered electrons (BSE) is desired, a potential that is negativewith respect to the sample (6) is applied to the collector grid. Thesecondary electrons, which emerge from the sample (6) with a smallenergy of a few electron volts, are kept away from the scintillator (3)by the collector grid due to this negative potential. Consequently, onlythose electrons strike the scintillator (3) that can overcome thecounter-potential of the collector grid because of their higher kineticenergy. These are the electrons which were backscattered at the sample(6). These backscattered electrons are accelerated between the collectorgrid (5) and the scintillator (3) and because of their high energyproduce photons in the scintillator (3), to be conducted by the lightguide (2) to the photodetector (1) and detected there.

If the detection is desired of the secondary electrons released from thesample (6) by the primary electrons PE, a positive potential withrespect to the potential of the sample (6) is applied to the collectorgrid (5). The secondary electrons released from the sample (6) areextracted by means of this positive potential of the collector grid andare then accelerated between the collector grid (5) and the scintillator(3) to the scintillator potential. In this case, the acceleratedsecondary electrons, because of their high kinetic energy, also releasephotons from the scintillator (3), to then be detected by thephotodetector (1). Admittedly, with a positive potential of thecollector grid with respect to the sample potential, electronsbackscattered at the sample (6) also strike the scintillator (3);however, only a very small solid angle is subtended by all the electronsbackscattered at the sample (6), while the secondary electrons, due totheir lower kinetic energy when they leave the sample (6), are detectedalmost independently of the direction in which they leave the sample(6). Because of this, the signal detected by the photodetector (1) whenthe collector grid potential is positive with respect to the samplepotential is primarily determined by the secondary electrons leaving thesample (6), while the electrons backscattered at the sample (6) causeonly a comparatively small signal background.

When the detector is operated under high chamber pressures (FIG. 2), thescintillator (3) is at the potential of the sample (6). The collectorgrid at the same time has applied to it a variable potential between 0and +400 V with respect to the potential of the sample (6). If only thedetection of the electrons backscattered at the sample (6) is desired,the collector grid is placed at the potential of the sample (6). Theelectrons backscattered at the sample (6) and striking the scintillator(3) because of their backscattering angle again produce photons in thescintillator (3), as in high vacuum operation, because of theirrelatively high kinetic energy, and the said photons are detected by thephotodetector (1). If on the contrary the detection of secondaryelectrons is desired, the collector grid is placed at a potential whichis positive with respect to the sample potential (6). The secondaryelectrons leaving the sample (6) are then accelerated toward thecollector grid and produce the known gas cascade and the photonssimultaneously leaving the gas cascade, by collision with the gas atomson this path. These photons pass through the electrically conductivecoating (4), which is transparent to visible light, and the scintillator(3), likewise transmissive for visible light, and are then conducted bythe light guide (2) to the photodetector (1). Additionally oralternatively to detecting the photons produced, the electron currentproduced by the gas cascade and detected with the collector grid or withthe electrically conductive coating (4), can be made use of for signalrecovery in this mode of operation.

The changeover of the application of potential to the scintillator takesplace automatically by the control (13) in dependence on the pressure inthe sample chamber determined by the pressure sensor (12). If thechamber pressure exceeds the preset changeover pressure, thescintillator potential is automatically switched off or reduced, so thatvoltage overstrikes are excluded; if the chamber pressure falls belowthe changeover pressure, the preset scintillator potential is againapplied to the scintillator (3).

The detector in FIG. 3 has in principle the same construction as thedetector in FIG. 1. The components in FIG. 3 that correspond to those inFIG. 1 are therefore given the same reference numerals. Reference istherefore made to the previous description of FIG. 1 for a detaileddescription of these components and of the operation of this detector inhigh vacuum.

In the embodiment according to FIG. 3, in addition to the voltage source(8) for the application of potential to the collector grid (5) and avoltage source (9) for setting a variable sample potential, a furthervoltage source (7) is provided by means of which the electricallyconductive coating (4) of the scintillator (3) can be placed at apositive potential US with respect to the collector grid (5). Thepotential of the electrically conductive coating (4) with respect to thecollector grid (5) is thus variable. By applying this additional voltageUS between the electrically conductive coating (4) of the scintillator(3) and the collector grid (5), a further gas cascade is formed betweenthe collector grid (5) and the scintillator (3). For signal recovery,both the light signal detected with the photodetector (1), and also theelectron current on the collector grid (5) and/or on the electricallyconductive coating (4) can furthermore be detected, for which purpose acorresponding current amplifier (10) is connected to the collector grid(5) and a second current amplifier (11) is connected to the electricallyconductive coating (4). By variation of the voltage of the collectorgrid (5) with respect to the sample potential on the hand, and thevoltage between the electrically conducting coating (4) and thecollector grid (5), a distinction can be made with higher accuracy, ascompared with the embodiment according to FIGS. 1 and 2, between thesignals produced by secondary electrons and the signal produced bybackscattered electrons.

In particular it is also possible in this embodiment to place thecollector grid (5) at only such a weakly positive potential with respectto the sample potential, and the conductive coating (4) of thescintillator at such a high positive potential with respect to thecollector grid (5), that the secondary electrons coming from the sampleare indeed efficiently extracted by the potential of the collector grid,but however no gas cascade, and the secondary electron multiplicationassociated with it, arises between the sample and the collector grid,but the gas cascade first arises between the collector grid (5) and thescintillator. Since the gas cascade is thereby localized in theneighborhood of the scintillator and the photons arising when the gascascade is formed arise in this localized space, the detection of thephotons takes place with a higher efficiency. Furthermore, by a separatecontrol of the pressure between the collector grid and the scintillator,e.g. by constructing the collector grid as a pot with a relatively smallaperture facing toward the sample and forming a “pressure stagediaphragm”, and by means of a specific gas inlet into the interior ofthe pot, it is possible to set a pressure, deviating from the chamberpressure and to a certain extent independent, between the collector gridand the scintillator. A formation of the gas cascade that is to thisextent independent of the pressure in the chamber, and a correspondinglyindependent amplification of the secondary electrons and photons,thereby result. A multiplication of the secondary electrons can also beattained by these measures when the pressure in the specimen chamber isitself too small for the formation of a gas cascade.

The embodiment in FIG. 4 has a similar construction as the embodimentexample in FIG. 3, but is formed tapering conically to a point in thedirection toward the sample, and thus on the side remote from thephotodetector. It has a light guide (34), on which a scintillator (30)is set on the sample side. The scintillator (30) is provided on thesample side with an electrode (26), transmissive to light and formedeither as a thin metal layer or in grid form.

A needle electrode (24) tapering to a point on the sample side andextending in the direction of the sample is received in a central recess(27) in the sample-side front surface of the scintillator (30). Therecess (27) serves exclusively for the electrical insulation of theneedle electrode (24) with respect to the scintillator electrode (26).

A middle electrode (22) is received externally on the light guide (34)and surrounds the needle electrode (24) in pot form, and is formedconically converging on the sample side, so that a sample-side aperture(23) with an aperture diameter between 0.5 and 5 mm results for theentry of electrons. The middle electrode (22) is mirror-coated on theinside.

In a special embodiment of the embodiment, the inner electrode (22) issurrounded by yet another outer electrode (20), likewise running to apoint in the direction toward the sample and likewise forming an inletaperture (21) on the sample side. Between this outer electrode (20) andthe middle electrode (22), the gas and its pressure in this interspacecan be set by means of a gas inlet (19), partially independently of thegas and pressure in the sample chamber. When a somewhat higher prevailsin the detection chamber, and thus in the interspace between the middleelectrode (22) and the outer electrode (20), than in the sample chamber,this has the advantage that the gas diffusing out of the sample chamberinto the detection chamber is constantly flushed out of the detectionchamber again.

The outer electrode (20) serves on the one hand to screen off withrespect to the primary electron beam (PE) the high voltage potentialthat is applied to the scintillator electrode (26) in high vacuumoperation. Furthermore the outer electrode (20) serves for attractingsecondary electrons from the sample to the aperture (21). By means ofthe tapering constructional form of the outer electrode (20), theundesired signal contribution due to secondary electrons produced bybackscattered electrons in the gas of the sample chamber is kept as lowas possible, since only such secondary electrodes pass through theaperture which are situated at not too great a distance from theaperture, i.e., the weak far field of the pointed outer electrode makessure that the secondary electrons pass through the aperture (21) onlyfrom a narrowly limited volume.

The potential U1 of the outer electrode (20) is to be adjustable in arange of 0-500 V positive with respect to the sample. A stronglypositive potential over 200 V has the advantage that a gas cascade isthereby produced in the sample chamber and runs to the aperture (21) ofthe outer electrode. The detector efficiency is thereby increased, inthat more electrons reach the detection chamber. Furthermore, theelectrode which enter the detection chamber—particularly with not toohigh a gas pressure—have a higher average kinetic energy, so that theyare little affected by the transverse component of the electric fieldtransverse of the rotation axis of the detector—which pushes theelectrons from inside to the outer electrode. With a weak positivepotential below 50 V positive with respect to the sample, a morefavorable course of the electrical field can be set, in which thesecondary electrons, during or after passing across the aperture (21),are pushed little or not at all against the outer electrode (20).

For reducing the indirect signal portion which is provided by thebackscattered electrons due to those secondary electrons which areproduced by collision of the backscattered electrons with the pole shoe(28) of the objective lens, it is helpful if the potential of the sampleis slightly, i.e., about 50 V, negative with respect to the potential ofthe pole shoe. By a wire gauze electrode at sample potential (or atanother potential, which is nearer to the potential of the sample thanto the potential of the pole shoe), between the sample and the poleshoe, it can be attained that the space immediately above the pole shoeis nearly field-free and the extraction of the secondary electrons bythe further electrode (20) is not adversely affected.

The middle electrode (22) likewise serves to keep small the proportionof secondary electrons that are pushed against the outer electrodes, inthat the secondary electrons after entering the detection chamber arefurther deflected in the direction toward the scintillator. For this,the potential of the middle electrode is 30-500 V positive with respectto the potential of the outer electrode (20).

In the case that the outer electrode (20) is not present, its functionis of course fulfilled to some extent by the middle electrode (22).

The detection efficiency for photons is increased by the internal mirrorcoating of the middle electrode (22), in that those photons that strikethe inner surface of the middle electrode are reflected toward the lightguide end. A slightly absorbing, light-scattering internal coating ofthe middle electrode has a similar effect, though with lower efficiency,since with a mirror coating the photons can be deflected specificallytoward the light guide.

When a potential difference with respect to the ambient potential isapplied to the needle electrode (24), a high field strength occurs atthe needle point. This ensures that at a high gas pressure the greaterportion of the potential difference is situated on a short path, so thatthe product of gas pressure and path can be set to the optimum value fora strong gas cascade, and the gas cascade arises predominantly in thedetection chamber. In operation with high pressure in the samplechamber, the needle electrode acts as a collector electrode. With acurrent amplifier connected to the needle electrode, the secondaryelectron current can also be detected, so that the light guide andphotodetector can then be dispensed with if the detector is only to beused at high chamber pressures.

In principle, the same result as with the needle electrode (24) can beattained when instead of it an electrode of plural thin wires (wirethickness below 0.3 mm) stretched parallel to the scintillator electrode(26), or a wire gauze electrode, is arranged closely before thescintillator electrode (26), at a spacing of less than 20 mm, preferablyat a spacing of less than 10 mm. In the latter case, the distancebetween the wire gauze electrode and the scintillator electrode (26)determines the high field strength.

In operation with high pressure (above 500 Pa) in the sample chamber,the potential U3 of the needle electrode (24) is to be at least 200 Vpositive with respect to the potential of the middle electrode. Ataverage pressures between 1 Pa and 500 Pa, the potential of the needleelectrode (24) is to lie between the potential of the middle electrode(22) and the potential of the scintillator electrode (26); it is therebyattained that the gas cascade is somewhat spread apart. In high vacuumoperation, the potential of the needle electrode (24) is likewise to liebetween the potential of the middle elect rode (22) and the potential ofthe scintillator electrode (26), but it can however also coincide withthe potential of one of the two electrodes (22, 26).

The potential U4 of the scintillator electrode (26) lies at the highvoltage potential when operating in high vacuum, as in the otherembodiments. At middle chamber pressures, the gas cascade is to end atthe needle electrode (24). At high pressure in the sample chamber, thepotential of t he scintillator electrode (26) lies between the potentialof the needle electrode (24) and that of the middle electrode (22). Bythis means, a course of the field is attained which on the one hand ishelpful as an extraction field in the aperture of the middle electrode(22). On the other hand, the course of the field guides the secondaryelectrons into the neighborhood of the needle electrode, where they areattracted by the positive potential of the needle electrode.

As in the other embodiments, the scintillator (30) acts in the highvacuum region to produce photons, which are then amplified by aphotomultiplier and detected.

The gas feed gives the possibility in the high vacuum region, as inoperation with high chamber pressure, of producing a gas cascade in thedetection chamber. Furthermore, the gas of the detection chamber can bechosen independently of the gas in the sample chamber, and thereby a gaswith a high amplification factor can be chosen for secondary electronmultiplication, for a strong gas cascade.

1. A detector for varying pressure ranges in a specimen chamber of aparticle beam device, wherein the detector is arranged and adapted fordetection of electrons and light.
 2. The detector according to claim 1,wherein the detector comprises a scintillator to which a high voltagepotential is appliable, and a photodetector, the scintillator being atleast partially permeable to light.
 3. The detector according to claim2, wherein the scintillator comprises an electrically conductive coatingin grid or strip form.
 4. The detector according to claim 2, wherein thescintillator comprises an electrically conductive coating that ispermeable to light.
 5. The detector according to claim 1, furthercomprising a light guide.
 6. The detector according to claim 5, whereinthe light guide comprises scintillator material.
 7. The detectoraccording to claim 2, further comprising a collector electrode connectedbefore the scintillator.
 8. The detector according to claim 7, whereinthe scintillator and the collector electrode are controllablepotentials, independently of each other.
 9. The detector according toclaim 7, wherein the collector electrode is arranged and adapted forapplication of a variable potential, positive with respect to the samplepotential.
 10. The detector according to claim 7, wherein thescintillator comprises a conductive coating, further comprising currentamplifiers that are connected to at least one of the collector grid andto the conductive coating of the scintillator.
 11. The detectoraccording to claim 8, wherein the conductive coating of the scintillatoris arranged and adapted to have a potential applied with respect to thecollector electrode so that a gas cascade arises between the collectorelectrode and the conductive coating.
 12. The detector according toclaim 1, further comprising a needle electrode or an electrode of thinwires on a sample side of the scintillator.
 13. The detector accordingto claim 1, further comprising a scintillator and an electrodesurrounding the scintillator in a form of a pot that tapers conically toa point on a side remote from the scintillator and comprises an openingon a side remote from the scintillator.
 14. A particle beam device,particularly a scanning electron microscope, comprising a samplechamber, with a variable pressure, an electron optical system forproduction of a focused electron beam (PE) and a detector according toclaim
 1. 15. The particle beam device according to claim 14, furthercomprising a pressure meter in the sample chamber so that theapplication of potential to the scintillator takes place in dependenceon the pressure in the sample chamber.
 16. The particle beam deviceaccording to claim 15, that is arranged and adapted so that at pressuresin the sample chamber below a changeover pressure between 10⁻³ hPa and10⁻² hPa, a potential of greater than 1 kV positive with respect to thepotential of the sample is applied to the scintillator, and at pressuresin the sample chamber above the changeover pressure, a potentialquantitatively smaller than 1 kV, preferably smaller than 0.5 kV,positive with respect to the potential of the sample is applied to thescintillator.
 17. The particle beam device according to claim 15,wherein the sign of the potential of the collector electrode isreversible.
 18. The particle beam device according to claim 16, that isarranged and adapted so that at pressures above the changeover pressurein the sample chamber, a potential of 0 V or +400 V with respect to thepotential of the sample is applied to the collector electrode.
 19. Amethod for the detection of the products of reciprocal effects in aparticle beam device under variable pressure conditions, comprising thestep that under high vacuum conditions the light arising when theproducts of interaction strike a scintillator, and the step that atambient pressure or low vacuum conditions, the light arising when theproducts of interaction interact with gas molecules, are detected withthe same photodetector and then evaluated.
 20. The method according toclaim 19, comprising the step of using a detector according to claim 1.21. The particle beam device according to claim 16, wherein thepotential is quantitatively smaller than 0.5 kV.